14:3-5 (ESV)
3 and they were singing a new song before the throne and before the four living creatures and before the elders. No one could learn that song except the 144,000 who had been redeemed from the earth. 4 It is these who have not defiled themselves with women, for they are virgins. It is these who follow the Lamb wherever he goes. These have been redeemed from mankind as firstfruits for God and the Lamb, 5 and in their mouth no lie was found, for they are blameless.
Israel will be the firstfruits of those redeemed from the earth of mankind. Those in the body of Christ are the firstfruits of those saved and made holy by their faith in Christ. From His body will come the bride of Christ.
Only Israel can sing the the song of the firstfruits of those who dwell on earth. The body of Christ are those who have become the firstfruits of those who dwell in heaven.